What is it that you don't get?
For your question in the title "Who owns Bitcoin", nobody owns bitcoin because it is decentralized, meaning no central body controls nor governs it. No one can own all the Bitcoin in the world as Bitcoin has a total supply of 21,000,000 and as of this writing the circulating supply in coinmarketcap is 16,946,875 which means there is still 4,053,125 Bitcoins which are not yet mined.